During the summer of 2000 the Texas Air Quality Study (TEXAQS-2000) investigated the factors that control the formation and transport of air pollutants along the Gulf Coast of southeastern Texas during periods of high photochemical activity. When winds came from the Gulf of Mexico, the LaPorte Airport site was upwind of most of the nearby petrochemical refineries that line the shipping channel between Galveston Bay and central Houston. EPA scientists used a variety of real-time instruments at LaPorte to measure particle number and size distributions, light scattering and absorption. For speciation of semi-volatile organic compounds EPA, LBNL, Environment Canada and the Northwest PM Center collaborated to measure the gas/particle partitioning at LaPorte and two other locations in Greater Houston, using high capacity Integrated Organic Gas and Particle Samplers (HiC IOGAPS) of LBNL design. The particle mass loading ranged from 10 - 100 ug m^(-3) during the study. The highest particle mass loading was observed during a period when brushfires impacted Houston with wood-smoke. However, more and smaller ultrafine particles were associated with unique plumes moving in and out of the sampling site near periods of high ozone than with the brushfires. Although light-absorbing particles were elevated during both types of episodes, particles with enhanced UV absorption were associated only with wood smoke. Ozone-related ultrafine particles did not cause elevated absorption of ultraviolet light. A detailed analysis of the semi-volatile hydrocarbon compounds using the HiC IOGAPS during the high ozone, wood-smoke episodes, as well as a contrasting cleaner period, will be presented. Gas/particle partitioning of alkanes and polycyclic aromatic hydrocarbons during these episodes followed the predictions of Junge-Pankow theory.